UntitledMr Collinson's Science 1
Pascal's Law What is Pascal's Law? The pressure in an enclosed fluid is uniform 
throughout.
How does Pascal's law help us explain what happens when there is a leak  in a pipe?  At what point does the fluid stop leaking from a pipe?
The leak would stop if the pressure inside the pipe was lowered to match  the air pressure on the outside.  However, often times (as would be the  case to the right) there is more fluid constantly being pushed through the  pipe, so it will leak until the source is cut off.
When a pipe is punctured, or if it is not  sealed properly, the fluid will rush out of  the pipe.  This is because the fluid is  under pressure, and so is pushing  outwards on the pipe.  With no pipe wall  there to hold it back, it exits.
Mr Collinson's Science 2
Pumps In the case of a water line, like the copper pipe shown on the previous  slide, water is constantly "pumped" through the line.
A pump is a device that forces fluids into an area.  By forcing the fluid  into an area it creates pressure in the fluid.
The water in your home is an example of this.  Water is pumped  through the city water lines, putting it under pressure.  When your  faucet is closed, the water is blocked from escaping.  Once you open  the faucet, the water is pushed out of the tap by the pump.  As more  and more faucets are opened, more water is released.  This means the  pump has to supply more water.  If the pump can not keep up, you will  lose "water pressure."  The water will not come out as quickly, as there  is not as much pressure in it.
Hydraulics Fluids under pressure are not just used to supply things like water.  We can  use the force created by this pressure to make powerful tools.
Hydraulics The study of pressure in liquids
Hydraulic System A device that transmits a force through a liquid by  using Pascal's law of constant pressure
Here is a video that discusses an example of a hydraulic system, "The Jaws of Life."
Fluid, under pressure, is used to move a pair of metal arms.
YouTube Link
Mr Collinson's Science 3
Pneumatics Although liquids do not compress as easily, sometimes gases are more  practical to use.  These systems are called pneumatic systems.
Pneumatics The study of pressure in gases
Pneumatic System A device that transmits a force by releasing a gas   that is stored under pressure
Here are a few examples of things that use pneumatic principles.
Pressure Please use the remaining time to complete the following list of work:
1. Fluids Math (should be done and checked by now) 2. Pressure Questions (answer key available) 3. Compressibility Questions (discuss answers with a peer)
If all of this is complete, you may use any remaining time to work on  your hydrometer project or other work.
Attachments
Pressure
Pressure is the amount of force exerted per unit area on a surface that is perpendicular to the
force. In mathematical terms:
Force essure Pr
Pressure is measured in Pascals, where 1 Pascal is 1 Newton per square meter. More commonly
used is the Kilopascal, which is 1000 Newtons per square meter.
For example, if a person has a weight of 490 N (50 kg x 9.8 N/kg – this is gravitational force)
and there feet take up an area of 400 cm 2 , then the pressure they exert on the ground may be
calculated as follows:
Force = 490 N
2
Pressure = ?
Complete the following questions related to pressure.
1. A block, resting on the ground, has a cross sectional area of 2 m 2 is being pushed with a
force of 100 N. What is the pressure exerted by the block on the ground?
= 100 =
∴ The pressure on the ground
= 2 2 = 100
2 2 is 50 .
=? = 50
kPaessure 25.12Pr
2. An aquarium holds 100 L of water (recall that 1 L of water weighs 1 kg). The base of the
aquarium is 1 m by 0.5 m. What pressure is exerted on a table by the filled aquarium?
100 L of water has a mass of 100 kg. The area of the aquariam can
To find the weight of an object you be calculated, as both the length
multiply its mass by the gravitational and width are provided
constant
=
= 100 × 9.8 ⁄ = 1 × 0.5
= 980 = 0.5 2
= 980 =
∴ The pressure on the table
= 0.5 2 = 980
0.5 2 is 1960 .
=? = 1960
3. Tom’s hand print is 30 cm 2 but Sean’s handprint is only 20 cm
2 . If Tom is able to push
with a force of 70 N and Sean can push with a force of 50 N, who can exert a larger
pressure on an object?
∴ Tom can push with a
= 30 2 = 70
0.0030 2 pressure of 23. 3 .
= 0.0030 2 = 23 333. 3
=? = 23. 3
Sean
∴ Sean can push with a
= 20 2 = 50
0.0020 2 pressure of 25.0 .
= 0.0020 2 = 25 000
=? = 25.0
∴ Sean is capable of exerting a larger pressure on an object.
4. If a box is applying 24 kPa of pressure on a table and the area of the box is 80cm 2 , what
must the weight of the box be?
=? =
= 80 2 = × box is 192 .
= 0.0080 2 = 24 000 × 0.0080 2
= 24 = 192
= 24 000